1. Field of the Invention
This invention relates to new and useful improvements in adjustable vacuum forming molds for sheet plastic materials and more particularly to molds for forming sheet plastic into liners for truck beds.
2. Description of the Prior Art
The prior art discloses a number of U.S. patents, such as Lorenzen U.S. Pat. No. 3,814,473, Nix U.S. Pat. No. 3,881,768 and the like in which a solid continuous plastic sheet liner is provided for the beds of pick-up trucks and the like. Such liners have been prepared by vacuum forming of heated plastic sheet material and have been generally formed to fit the interior contours of pick-up trucks or the like.
In the past, vacuum forming molds for forming truck bed liners of the type referred to above have been made to form only a liner of selected size and shape fitting a single make and body style of pick-up truck.
Ercolano U.S. Pat. No. 3,868,288 discloses a double walled, vacuum forming mold for forming appliques of thermoplastic sheet material onto a substrate.
Walter U.S. Pat. No. 4,052,241 discloses a method and apparatus for vacuum forming a flexible material such as a thermoplastic sheet to fit a contoured substrate.
Alter U.S. Pat. No. 4,065,337 discloses a contoured double walled vacuum forming mold for forming sheet plastic into a contoured structure such as a boat hull.
Childress U.S. Pat. No. 3,770,546 discloses an apparatus and method for vacuum forming sheet plastic material, including movable plugs for assisting in the forming of sharp corners.
Smith U.S. Pat. No. 4,053,667 discloses the use of vacuum for laminating sheet plastic material to other objects wherein separate stiffening members are laminated between the plastic sheet covering and the substrate.
Krutzikowsky U.S. Pat. No. 3,540,113 discloses a method and apparatus for vacuum forming a one piece plastic body to be used as the main body portion of a camper truck trailer.
The prior art methods and apparatus used for forming sheet plastic material by vacuum forming and more particularly for the vacuum forming of plastic sheet liners for the beds of pick-up trucks have been of a design which permits the formation of only a single style and size of truck bed liner. As a result, it has been necessary to make a separate and distinct vacuum forming mold for each different make and size of pick-up truck for which a liner is needed. There has been a substantial need for a single multipurpose vacuum forming mold which is capable of forming sheet plastic material into liners for a variety of sizes and makes of pick-up trucks.